You can subscribe to this blog

Friday, December 24, 2010

Hydrangea spp., Hydrangeaceae

Season's Greetings and Best Wishes for 2011 to all readers of this blog.

I know some people who think that Hydrangea flowers are more attractive when dead that alive. It's a sentiment that I have some sympathy with...

... because I don't find the heavy, long-lasting infloresences of mop-headed Hydrangea macrophylla cultivars particularly attractive, but when winter has done its work on the dead flower heads the skeletonised florets, like those in the first photograph, are transformed into something rather delicate and beautiful.

Hydrangea infloresences are an interesting example of division of labour, where the central mass of short-lived fertile flowers, bearing stamens, stigmas and ovaries, have no particular visual advertising to attract insects but devolve that job to the large sterile florets, that surround the edge of the inflorescence like orbitting satellites. Petals wilt as soon as a flower is fertilised but since that outer ring of sterile advertising florets can never be fertilised they last indefinitely, throughout the whole flowering period and often right through the winter as skeletonised petals.

The arrangement is delightful in some of the larger species like H. aspera (also known as H. villosa) when it's grown in an open, woodland garden.

Advertising all those fertile florets with just a handful of sterile florets is a very efficient way for the plant to attract its pollinators, but it's hardly surprising that plant breeders have hybridised and selected species for large numbers of sterile, long-lasting florets for maximum impact in a shrub border, reversing nature's economical use of advertising in the quest for maximum visual impact.

Monday, December 20, 2010

Tephrocactus articulatus var. papyracanthus, Paper-spined Cholla

This must surely be one of the most intimidating of all plants - the Paper-spined Cholla Tephrocactus articulatus var. papyracanthus. It comes from Argentina and those sabre-shaped spines that look so lethal are about eight centimetres long, but they're not as dangerous as they look. They really are like paper and simply bend under the slightest pressure; you'd be hard-put to draw blood with them. The tufts of tiny bristle-like hairs called glochids that you can see at their base are far more of a problem. They have barbed tips and are intensely irritating when they embed themselves in your fingers.The easiest way to remove them from flesh is to use a piece of adhesvive tape to pull them out.

Paper-spine cholla ( or the 'Edward Scissorhands' cactus, as my kids used to call it) is a slow-growing relative of the prickly pear cactus and is easily propagated by breaking off one of the jointed stem segments and rooting it in well-drained, gritty compost - but be sure to watch out for those nasty little glochids.

Thursday, December 16, 2010

Clematis cirrhosa

My Clematis cirrhosa, whose straggly stems climb through a crab apple tree in my garden, managed to produce just this single flower before the first spell of freezing weather arrived. There are more well developed flower buds on it but the icy weather has returned and it's doubtful if they'll open now. Bearing in mind that this species hails from the Balearic Islands it's a small miracle that it survives here at all. It came through last winter safely so I'm optimistic that it'll do so again.

In milder parts of southern England there have been several reports of bumblebees that emerge on mild days in mid-winter visiting these flowers, along with Mahonia blossoms, but that's unlikely during this winter's icy blast.

Monday, December 6, 2010

Chinese lanterns,Physalis alkekengi var.franchettii

My grandmother in Sussex used to grow Chinese lanterns Physalis alkekengi var. franchettii to perfection, but I've always struggled to grow them up here in North-East England, not least because the slugs and snails zero in on them almost as soon as new shoots appear in spring. Looking at the natural distribution of the plant - southern Europe and eastwards across drier parts of Asia, it's not surprising that I haven't been able to grow these well. Gran's garden was mostly flint and chalk and she grew them in a sun-drenched spot in gravel at the base of a south-facing bay window, which provided a fair approximation of the Mediterranean climate and soils that this plant enjoys.

The orange papery 'lantern' is formed from the sepals (collectively the calyx) of the flower that inflates once it has been pollinated, enclosing the....

......shiny red berry within. The dried plant makes a colourful winter decoration but if you leave some outdoors the softer parts of that inflated calyx rot away surprisingly quickly, so that by Christmas you have ....
... only the skeleton of veins left which - with a light spray of gold laquer - makes a delightfully intricate Christmas tree decoration.

There seems to be some taxonomic uncertainty surrounding this plant, which is sometimes known simply as P. franchettii. According to the late Graham Stuart Thomas - a gardener who really knew his perennials - P. franchettii has more pointed lanterns - like those in the first photo above - compared with the rounder P.alkekengi, in the skeletonised example above but, since he also mentions that they hybridise, it's reasonable to conclude that they are merely varieties of the same species.

Wednesday, December 1, 2010

Madagascan Lace Plant, Aponogeton madagascariensis

I've never seen a living specimen of Madagascan lace plant Aponogeton madagascariensis but I found this pressed specimen in the herbarium of Durham University's School of Biological and Biomedical Sciences. I suspect it's a very old specimen as it still bears an old Latin name for the genus, Ouveranda. These look like skeleton leaves but in fact they are intact - during the final stages of development of the expanding leaves of this aquatic plant the cells between the veins die, during the process of programmed cell death (apoptosis) leaving a network of veins surrounded by living photosynthetic cells. The development of the leaf has recently been studied in great detail and you can read the scientific paper from the American Journal of Botany that describes the process (which also includes photos of the whole, living plant) by clicking here.

In this close-up of a portion of the pressed leaf you can see the ladder-like arrangement of leaf veins that are surrounded by photosynthetic tissue. Apparently this plant is a popular but challenging species to grow for tropical aquarium enthusiasts and you can read an account of its cultivation here.

Saturday, November 27, 2010

Tibouchina urvilleana

Our garden is currently hidden under several inches of snow but the Tibouchina urvilleana plants in our small conservatory, which would be more at home in tropical Brazil than in freezing north-east England, are in full flower. Each bloom only lasts for a couple of days but they are produced in a long succession through the darkest months of winter. These plants have very unusual flowers, with two types of stamens. The lower, claw-shaped ones are the genuine article, producing pollen that is squeezed out of a pore in their tip when they are pushed downwards, but the upper ones with pale tips are sterile 'food' stamens that attract bees. They use the pollen- bearing stamens as a landing pad and unwittingly transport the pollen.

Tibouchina urvilleana grows into a greenhouse shrub but old, woody plants soon become shapeless and their brittle stems easily snap. I've found that the best way to grow them is to take semi-ripe cuttings in summer, when they root very easily, producing compact plants with plenty of 3 inch diameter flowers from November onwards.

Tuesday, November 23, 2010

Stinking iris,Iris foetidissima

Stinking iris Iris foetidissima has two memorable features. The first is the vibrant orange seeds that are revealed when the seed pod bursts open. These make excellent decorations and I have a vase of them on my desk as I write.
Each seed is surrounded by a soft orange aril, which slowly dries and wrinkles once it's exposed to air.
The other memorable feature isn't the flower, which is unspectacular by the standards of many irises, but the smell. If you crush the foliage between finger and thumb you release an aroma that's reminiscent of roast beef or, perhaps more accurately, the exaggerated beefy smell of a packet of roast beef-flavoured crisps. The species is sometimes known as roast beef plant.

Iris foetidissima is easy to grow from seed and thrives on a dry, sunny bank in my garden, producing seed pods for winter decoration every year.

Wednesday, November 10, 2010

Barley, Hordeum vulgare

Gardening with grasses has become popular in recent years and garden centres are full of examples - many of which, I have to say, look pretty unexciting to me. So I've always been surprised that gardeners don't cultivate some of our cereals, like wheat, rye, oats and the barley Hordeum vulgare pictured above for their decorative properties. Maybe it's just that they are such familiar plants in the landscape, but for sheer architectural beauty they really are very attractive - and the barley variety that I recently found preserved on an old herbarium sheet in Durham University School of Biological and Biomedical Sciences must have been especially so when it was alive and growing.

This particular plant has purple grains. Let me begin by quoting the attached label, that outlines its provenance.

Huskless Barley from Thibet (sic)
This ear of barley was grown at Burton-on-Trent by me in 1890 from seed given by the late Horace T.Brown,F.R.S. He got it from the late Thistleton Dyer, Director of Kew Gardens, who got it from Mr. Duthie of Sharanpur Botanical Gardens. He says the seed came from Poo in Thibet about the year 1881 when it was introduced into the Punjab, with other varieties. Dr. H.T.Brown says in some notes on this barley (Transactions of the Burton Natural History Society), “The colour is not diffused through the paleae, as in black Abyssinian or Scotch barley, but is confined to the integuments of the caryopsis. When microscopically examined, the inner protions of the pericarp immediately adjacent to the testa are seen to be charged with a very dark purple pigment, appearing in mass almost black. This pigment is fairly soluble in water, and probably consists of modified chlorophyll”.......“ The peculiar colour is not confined to the grain only, but occurs also in the nodes of the straw, which even at an early period of growth are very dark purple.” The colour appears to have faded somewhat during all the years that the specimen has been kept. I have tried two or three corns recently but failed to get any sign of germination. John E. Nowers. Jany 9 1928.

Huskless barleys like this, with grains that outgrow the papery glumes that normally enclose them tightly, have been cultivated for at least 8000 years and would have been prized by early farmers because their grains are easily separated from the papery chaff. The great 13th. century traveller Marco Polo, visiting the province of Badashan in what is now part of Afgahistan, mentions the crop:
"The mountains of this country also supply Saker falcons of excellent flight, and plenty of Lanners likewise. Beasts and birds for the chase there are in great abundance. Good wheat is grown, and also barley without husk."

When samples were brought to Britain in 1884 by the Mr. Duthie mentioned in the herbarium specimen label above, some were give to John McDougall, the flour miller, for evaluation as a malting grain. He noted that it sprouted well "but the colour comes off and so will not do for pale ales, but it would do well for stout. For feeding purposes it would be useful, although it would take time to remove prejudice for its colour"....

Regretfully Mr. Duthie conceded "The objection as to colour,alluded to in the report, is fatal to its value and will prevent it every being grown, except as a curiosity...."

There was, however, considerable interest in a white-grained variety of the huskless barley, which continues to this day in the malting industry, as evidenced by this research paper published in 2009 entitled 'Potential of Hull-less Barley Malt for use in Malt and Grain Whisky Production'. Huskless barley has come a long way in the last 8000 years.

Meanwhile, I'd love to get my hands on some viable seed of the purple-grained variety, to grow for its decorative properties in my garden.... as a curiosity, as Mr. Duthie suggested back in 1888.

The source of some of the above information is the Bulletin of Miscellaneous Information (Royal Gardens, Kew) No.23, 1888,pp. 271-273, which also contains more detailed information on Dr. Brown's anatomical studies on the grain.

Sunday, November 7, 2010

Lunaria annua, Honesty

Lunaria annua, commonly known as honesty or money plant, is an example of a species that's more attractive dead than alive. After the flattened fruits, known botanically as siliculas, have shed their seeds the central translucent septum of the silicula remains attached to the plant well into winter and looks especially striking when back-lit by low winter sunlight. The silvery appearance of the discs, resembling coins, accounts for the common names.

After pollination the ovary of honesty develops into a flattened disc-shaped silicula and when it's brightly lit by sunlight you can see the six kidney-shaped seeds developing inside. When it ripens the two outer walls separate from the central septum, the seeds blow away...........

 and only the papery central septum remains attached to the plant.

Honesty is a member of the cabbage family, Brassicaciae, whose members typically have four petals arranged in a  cross (explaining for the old name of the family, Cruciferae). The purple flowers of honesty aren't especially attractive, unless you happen to be an orange tip butterfly like this one, visiting to collect nectar.

Tuesday, November 2, 2010

Malus x zumi var. calocarpa 'Golden Hornet'

When you only have a small garden plants that perform more than once in a year are particularly valuable and there can't be many that put on a better display than Malus 'Golden Hornet'. In spring the branches almost disappeared under a dense covering of blossom that hummed with bees for about ten days ........

.... and this is the result of their work - a crop of crab apples that's so heavy that it threatens to break the more slender branches. Birds seem to leave these yellow fruits alone until the harder months of winter, when the apples have been softened by frost - and then the blackbirds move in. For most of the last decade the bark of my tree has been disfigured by an infestation of wooly aphids but it seems that last winter's prolonged frost and snow killed them. There's a lot to be said for the occasional really hard winter; this year the tree was pest-free

Saturday, October 23, 2010

Mahonia x media 'Charity'

I posted some pictures a couple of weeks ago of Sparmannia africana, which has remarkable stamens that spread outwards after they are touched. Here's another genus with touch-sensitive stamens - Mahonia - but in this case the stamens move in the opposite direction when they've been stimulated. The plant portrayed here is the hybrid between M.japonica and M. lomariifolia known as M. x media 'Charity', which has long racemes of lily-of-the-valley scented flowers that open in autumn and bloom well into winter, producing purple-blue berries that blackbirds love in early spring. In my garden I've watched over-wintering blackcaps pecking the flowers in this species and there a suspicion that they may be after the nectar, as the flowers don't attract any insects at this time of the year.

When the flowers first open the six stamens are spread wide, pressed against the petals, but if you touch the base of the stamen filament there's a slight delay and then they quickly move inwards, eventually coming to rest against the stigma.

Here's a flower where I poked the base of four of the six stamens with a pine needle. Three have closed on the stigma and the fourth is well on the way. The speed of movement depends on the ambient temperature - it was a cold day when I triggered these - but under warm conditions it takes about one second. Why do they do this? Hard to be sure, but I guess that it's likely that the foot of a visiting insect triggers the stamen movement, which forces pollen onto the insect's leg.

Mahonia and the closely related Berberis species have touch-sensitive stamens. Some botanists argue that species in these two genera should be amalgamated under the single genus Berberis, because they are so similar and some Mahonia and Berberis can form inter-generic hybrids (x Mahoberberis).

There's one other startling feature of these two genera that you can't see unless you prune off large branches. Their wood is bright yellow, due to the presence of a natural dye called berberine. The brilliance of the yellow wood is startling - even more so if you view it under ultra-violet light, because the berberine then fluoresces even brighter yellow.

Tuesday, October 19, 2010

Cucumis metuliferus, Cucurbitaceae

Each year I try to grow something a little bit unusual that's also edible and this year it was the turn of this weird fruit, the African horned melon Cucumis metuliferus. The plant resembled a small-leaved melon that rambled across the greenhouse staging, producing numerous small unisexual yellow flowers. Whenever a female flower appeared I carefully pollinated it but none seemed to be setting any fruit. It was only when I had given up and was about to throw the plant away that I parted the leaves and found this fruit, about 12cm. long and looking like something from another planet, revealing that one pollination had been successful. It looks like a vegetable version of a medieval mace and would probably make a good weapon, because those spines on the tips of the horns are very hard and sharp.

So, what does it taste like? Rather like cucumber, but with lemon juice added - quite refreshing - but the texture is strange. Each seed is surrounded by a semi-solid gelatinous coating and in the mouth it feels rather like eating frog spawn (not that I've actually eaten frog spawn, but this is what it must be like). Definitely an acquired taste. I spat out the seeds and will sow some next year, to see if it's any better second time around.
The plant is a native of Africa, although I gather that it's now cultivated in several countries and is known as kiwano on the US West Coast.

Thursday, October 14, 2010

Cercidiphyllum japonicum, Katsura tree

For most of the year you could walk right past a Cercidiphyllum japonicum tree without a second glance but in autumn it always stops people in their tracks - not just because of its autumn colour but because of its wonderful aroma. As the leaves turn yellow they produce a compund called maltol, which makes the whole tree smell of burnt toffee, rather like a toffee apple or candyfloss stall. Maltol is used as a flavour enhancer in the food industry, where it's known by the E number E636.
This specimen is in Durham University Botanic Garden but about five years ago I planted one in my own garden - and it has grown remarkably quickly. It's rather a large tree for a small garden - reaching 45m. in the wild, but it will be a while before mine becomes a problem. Katsuras, which are native to China and Japan, are supposedly frost-sensitive but mine came through last winter's prolonged snow and ice without any sign of damage. It will be interesting to see how the tree copes with a hot, dry summer (if we ever get another one here), as under those conditions it sheds all its leaves as a drought-avoidance mechanism, then refoliates when the rain returns - so can have two 'springs' in a single season.

This autumn year I collected a bag of those toffee-scented leaves to keep through the winter and sniff occasionally - as a reminder of that wonderful aroma on a warm, sunny afternoon.

Tuesday, September 28, 2010

Sparmannia africana, African Hemp

All plants are capable of gradual movement as a result of slow growth, but relatively few species can make the kind of rapid movements that we tend to associate with animals. The Venus fly trap Dionaea muscipula and the sensitive plant Mimosa pudica are the two species with rapid leaf movements that are most familiar but another fast-mover is African hemp Sparmannia africana. If you gently brush the cluster of golden stamens in the centre of the flower nothing happens for a second, than they move outwards, away from the stigma. The time delay between the photo above and that of the same flower whose stamens have been brushed, below, is about five seconds and you can easily see how the stamens have spread apart.
Presumably this is some kind of mechanism to aid pollination, although how it would do that isn't obvious. Similar stamen movements occur in Mahonia and Berberis flowers, although in those cases the stamens move rapidly inwards when they are stimulated.

Sparmannia africana comes from South Africa and makes a very fine house plant - if you have room for it. My plant grew too big for our conservatory and is now in Durham University Botanic Garden, where it has reached about three metres in height and is currently flowering and setting seed.

Friday, September 17, 2010

Mutants and Monstrosities

You don't need to be a gardener for very long before you discover that within every species there are always a few plants that don't conform to the norm. They're either mutants (where changes in their genes produce a different shape, form or colour of plant) or they're monstrosities (where there some external agency, like environmental stress or disease has led to abnormal growth).
Only mutants produce heritable changes, that will be passed on to at least some of their progeny. I would guess that the abnormal ox-eye daisy (Leucanthemum vulgare) above is a mutant. Some of its florets are spoon-shaped and since this abnormal plant turned up in my garden a few years ago others have appeared in subseqient years with the same characteristic, probably arising from seeds produced from those abnormal florets. Cultivars of a number of daisy-like species that have flowers composed entirely of spoon-shaped petals have been bred, so it's highly likely that this is a genetically controlled change in the pattern of petal development.

I'm pretty certain, on the other hand, that this two-headed ox-eye daisy is a monstrosity, the result of some agency that has interfered with the normal development of the flower and produced twin heads. Temperate-shock (i.e. frost) can sometimes do this.

This monstrous spear thistle Cirsium vulgare is the result of several flower heads becoming joined, side by side into a cock'scomb-like inflorescence, probably as a result of either stress during a critical phase of flower bud development or perhaps infection with a bacterium - Corynebacterium is known to cause a similar phenomenon, known as fasciation, in ...

Linaria purpurea...

Forsythia x intermedia, where it causes a switch in symmetry of the stem, from radial symmetry to flat, plank-like growth...

... and occasionally in herbaceous species like candelabra primulas ......

Some mutant forms of growth are widely cultivated for human consumption, like the cauliflower - which is a mutant inflorescence where the flower buds proliferate to the extent that they can no longer open properly.

My favourite monstrosity, though, is to be found in foxgloves Digitalis purpurea, where occasionally the last flower to form at the top of the floral axis results from fasciated growth of several flower buds. If you compare the monstrous flower on the left with the normal one on the right you can see that it has four stigmas, styles and ovaries, within a single tubular corolla - four flower buds fused to form a single flower.

Wednesday, September 8, 2010


Since this is the time of year when most plants in my part of the world are setting seeds, I thought I'd post a few images of these wonderful objects. This is one of the ripening seeds from my runner beans Phaseolus coccineus, with the testa and one of the cotyledons removed, revealing the embryonic plant inside. The cotyledons contain the store of proteins, carbohydrates and lipids that will provide sustanance for the germinating seedling until its first true leaves unfurl and begin to photosynthesise. In this image you can see that the rudiments of the venation in those first true leaves, that will transport sugars to other part of the young seedling, have already formed in the embryo. The embryo is attached to the cotyledons at its hypocotyl and the embryonic root points downwards and to the left. 

There's a heavy crop of oak (Quercus spp.) acorns in this part of Durham this year - it's a mast year. Oak acorns - technically nuts - germinate soon after they fall to the ground, anchoring themselves via their root but then suspending further growth until spring, when the shoot forms. If you are planning to plant oak trees, it's best to sow the fresh acorns soon after they fall.

Once seeds germinate their root needs to spear into the soil quickly, driven by the hydraulic force inside expanding cells. Here you can see the glistening root cap of a maize (corn) Zea mays seedling, producing the mucilage that lubricates its path between the abrasive soil particles. Further back, you can see the forest of root hairs, each a single elongated epidermal cell that makes intimate contact with the surface of soil particles and absorbs water and soluble minerals. Each root hair has a short life span, of perhaps a day, and new hairs are formed constantly behind the advancing root tip; collectively they constutive a vast absorptive surface.

Monday, August 30, 2010

Cyphostemma juttae, Vitaceae

About 20 years ago a South Africa botanist gave me a few seeds of this strange succulent, Cyphostemma juttae, which grows in rocky, arid parts of Namibia. It has taken all that time for the seedling to reach this size - about 70 cm. tall - on my windowledge and since it can grow to 2.5 metres tall in the wild it's still got some way to go, although it's under less than ideal conditions, in a flower pot.. Every winter it sheds those succulent leaves completely, leaving only the swollen stem - known botanically as a caudex - then regrows leaves in late spring. It first flowered about five years ago, but this is the first year that the flowers have produced fruits.

The stem constantly sloughs off layers of papery epidermis, which I suspect might have some role to play in reflecting intense sunlight.

The thick, lobed succulent leaves have a saw-tooth margin and each leaf lobe is about 15cm. long.

These small, glassy beads appear on the underside of the leaves, soon after they've fully expanded.

I've yet to discover whether they are crystalline sugar or resin - I suspect they are the latter.

One of the most remarkable aspects of the plant is that it is in the grape family and is commonly known as the Namibian grape or tree grape. You'd never suspect that until you take a look at the fruits, which turn purple when they ripen, but unlike the edible grape they are poisonous.